Many types of electronic and electrical equipment are sensitive to, and may be adversely affected by, electrical disturbances caused by magnetic fields, electric fields and plane wave fields. The increasing sophistication of the electrical and electronic apparatus necessitates emplacement in a facility which is grounded and which substantially prevents entrance of the spurious fields. The facility must, however, be suitable for human occupation with the result that doors and other entranceways must be provided both for access by personnel and various equipment. Similarly, building facilities, such as electric power, water, etc. must also be provided. The accessways, as well as the various facilities, usually require an opening in the building with the result that any opening wll permit the above-described fields to penetrate the building and thereby affect the equipment. Consequently, a system for securing the accessways and preventing the transmission therethrough of fields in desirable.
The electronic and electrical equipment located in the building is also responsible for the generation of fields and electrical signals. The equipment is, frequently, utilized under extremely secretive conditions and containment of the apparatus generated fields is required in order to prevent interdiction and interpretation of the fields by unwanted persons. The apparatus generated fields may be interpreted, with the result that the secretive work being carried out may be compromised. For this reason, the system for securing the accessways must also prevent the transmission of the apparatus generated fields throught the accessways.
Prior art sealing assemblies have utilized various electrically conductive sealing mechanisms for securing the accessways. These sealing mechanisms have a general drawback that the door which closes the accessway requires a bottom sealing assembly having substantial height. This bottom assembly necessitates the utilization of ramps on either side of the door in order to permit the movement of equipment and personnel through the door. The ramps are generally displaceable from a lower to an upper position with the result that passage through the accessway is very slow, particularly when a double accessway system is utilized. An additional problem is the fact that heavy equipment frequently bends or otherwise distorts the bottom sealing assembly and therefore adversely affects the security of the facility.
Sliding door assemblies have also been utilized for closing the accessways. The sliding doors also have the undesirable feature of the high bottom step. An additional problem with sliding doors is the need for some means of maintaining electrical connection between the door and the frame assembly. While electrically conductive springs and other such contact assemblies have been utilized in the above-described doors, such spring contact assemblies are frequently inappropriate with sliding doors.
A particular problem with both sliding doors, as well as conventional doors, is the necessity of a locking assembly. The door which closes the accessway must be capable of being easily opened and closed repeatedly, without adversely affecting the field shielding integrity of the door. Similarly, local building regulations require that the door be capable of being opened or closed with the exertion of minimal amounts of force, such as 20 lbs. The local building requirements also apply to the raised step because such a raised step may deny access to the building by handicapped persons. Consequently, local building regulations significantly impact the design of the door and its sealing assembly.
Schaller, U.S. Pat. No. 3,437,735, discloses a door construction for a shielded room. The door construction of Schaller discloses the utilization of leaf spring contact fingers around the periphery of the door or the door jamb. The door construction of Schaller, however, discloses the large raised step which has been found to be objectionable. Additionally, Schaller does not disclose the locking system for the door. A further problem with the Schaller design is the fact that the contact springs are made operational due to the pressure caused by closing of the door. One skilled in the art can appreciate that the greater the number of springs utilized, then the greater the amount of pressure required to close the door.
Based upon the above, one skilled in the art will appreciate that a new and unique shielded door assembly which conforms to local building regulations and which significantly inhibits the transmission of disruptive fields and signals through the accessway is advantageous. The disclosed invention provides a shielded door assembly utilizing both pressure operated and sliding contact spring assemblies to minimize the force required to open or close the door. Similarly, the high step has been eliminated and the field shielding integrity of the door has been improved through the utilization of parallel rows of leaf spring contact assemblies. Additionally, the door latching mechanism is disposed forwardly of the door panel and spring contact assemblies to thereby minimize the need for apertures in the door and the door frame, which would otherwise necessitate additional shielding protection.